"When corn is sitting there on the cob, all yellow and squishy, it's a vegetable. However, when corn is taken off the cob and dried out, it's a grain. Cornbread is made with corn meal, which makes it a grain. Popcorn is made with dessicated corn kernels, and so is also a grain. Canned or frozen corn, on the other hand, goes out of its way to retain corn's various ... on-the-cob qualities, and therefore qualifies as a ... vegetable."
Thanks again to The Brown Cow!
(I'd give them a link except s/he is evidently one of the more anonymous types. Bummer.)